An engine may be automatically stopped without a driver providing input to a device that has a sole purpose or function of stopping engine rotation so that fuel may be conserved. By stopping the engine, fuel consumption may be reduced at a time where engine efficiency may be less than is desired. One way to judge whether or not to stop an engine is to allow the engine to stop if the driver is applying a brake pedal and while vehicle speed is zero. If both conditions are met for a sufficient period of time, engine rotation may be stopped. However, if the driver temporarily releases or partially releases the brake pedal, the engine may be restarted so that the vehicle may launch. If the driver inadvertently releases the brake pedal, fuel conservation may not be realized and the driver may become aggravated. Additionally, if the vehicle is parked on an incline, the vehicle may move when the driver has no actual intent to do so.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating an engine, comprising: combusting an air-fuel mixture in an engine; stopping vehicle motion in response to a driver applying a brake pedal; applying vehicle brakes in response to the driver at least partially releasing the brake pedal; and stopping engine rotation in response to an indication applied braking force is sufficient to hold the vehicle from moving.
By applying vehicle brakes in response to a driver at least partially releasing a brake pedal and stopping engine rotation in response to an indication that applied braking force is sufficient to hold the vehicle from moving, the technical result that the engine may be turned off and may remain in a stopped state while the driver releases or partially releases a brake pedal may be achieved. However, if the braking force is determined to be insufficient for holding the vehicle in a stopped state, the engine remains operating so that engine creep torque and braking torque may be combined to limit vehicle motion. Further, by allowing the engine to operate, the engine may be allowed to increase vacuum for applying vehicle brakes. In this way, it may be possible to conserve additional amounts of fuel while holding the vehicle stopped until the driver intends to move the vehicle.
The present description may provide several advantages. Specifically, the approach may reduce engine fuel consumption by allowing an engine to remain in an off state for a longer period of time. Further, the approach may improve vehicle drivability. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.